This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 11-366180, filed Dec. 24, 1999; and No. 11-368273, filed Dec. 24, 1999, the entire contents of which are incorporated herein by reference.
The present invention relates to a 2D array type radiation detector having a plurality of detection elements in the form of a matrix which detect radiations such as x-rays as electrical signals, and an x-ray CT apparatus.
A medical x-ray CT apparatus has an x-ray tube and detector. X-rays generated by the x-ray tube are transmitted through an object to be examined and incident on the detector. The detector has a plurality of detection elements for detecting radiations such as x-rays as electrical signals. Detection elements can be classified into indirection conversion type elements, each designed to convert an x-ray into light by a phosphor (scintillator) and further convert the light into an electrical signal by a photoelectric conversion element (photodiode), and direct conversion type apparatuses, each using specific semiconductor characteristic, i.e., a photoconduction phenomenon in which electron-hole pairs are generated in a semiconductor and moved to its electrode by using x-rays. It is expected that direct conversion type apparatuses, which can achieve reductions in size, weight, and profile, will become popular.
As detectors for x-ray CT, single-slice type detectors are widely used. A single-slice type detector has a plurality of detection elements arrayed in a line. A multislice type detector constituted by single-slice type detectors arranged in a plurality of lines is also known.
FIG. 1 is a partial sectional view of a conventional multislice type detector. FIG. 2 is a schematic plan view of the detector. Referring to FIG. 2, an illustration of a scintillator is omitted. A plurality of photodiodes 92 are arranged on the rear surface of a scintillator 97. The plurality of photodiodes 92 are respectively connected to a plurality of integrators 95 through a plurality of wires 91. Selection switches 96 are provided in units of lines. Outputs from the integrators 95 are sequentially read out through the selection switches 96. The outputs of the selection switches 96 are electrically connected to a substrate 94 through bonding wires 93.
The integrators 95 store the signals detected by the photodiodes 92. Integral signals are sequentially output to the substrate 94 by the selection switches 96 through the bonding wires 93. The reason why the integral signals are sequentially read out by the selection switches 96 is that the number of bonding wires that can be formed on the substrate 94 is limited.
A great deal of attention has been paid to a 2D array type detector as a next-generation detector, which has more channels than the above multislice type detector, with the element pitch in the vertical direction (slice direction) being equal to the element pitch in the horizontal direction (channel direction).
To put this 2D array type detector into practice, various problems must be solved.
First, as the number of detection elements greatly increases as in the 2D array type detector, the precision in tiling the many elements into a specific shape deteriorates.
Second, as the number of detection elements greatly increases as in the 2D array type detector, the probability of the occurrence of faulty detection elements increases, and hence the yield decreases.
Likewise, as the detector is used for a long period of time, it is inevitable that some of many detection elements will fail. In this case, a detection element array or the overall detector must be replaced, resulting in a high cost. This is the third problem.
In addition, signal sampling is performed in CT an enormous number of times, e.g., several hundred or thousand times, per rotation. Therefore, the time permitted for 1-period signal read operation is very short. It is very difficult to complete reads of signals from many channels within such a short period of time. This is the fourth problem.
It is an object of the present invention to provide a radiation detector which implements tiling of many detection elements in the form of a matrix.
A radiation detector includes a plurality of detector modules detachably mounted on a detector base. Each of the detector modules has a plurality of element blocks permanently mounted on a module base. Each element block has a plurality of radiation detection elements formed on a signal substrate in the form of an mxc3x97n matrix. A detector module is made up of a plurality of element blocks. A radiation detector is made up of a plurality of detector modules. This makes it possible to tile many detection elements and manufacture a radiation detector with a wide field of view.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.